Rhythmicity in one form or another occurs in virtually all organisms ranging from man to microorganism, yet the biochemical and cellular basis for the generation and control of rhythms is not known. This project seeks to discover and define systems at the molecular level which are functionally involved in biological rhythm, especially daily (i.e. circadian) rhythms. During the past year our attention has been directed more and more to the possible involvement of membrane structure and function in the generation of rhythmic processes. In early 1974 we published a paper outlining these views and the experimental approaches which might yield information bearing on the question. In particular we propose that cell and membrane lipids be studied as a function of the time of day. In addition to this we plan to study rhythm mutants with regard to possible alteration in membrane structure and function, and/or lipids associated with the membranes which are related to rhythmicity. In this laboratory, we are using two unicellular forms - the dinoflagellate Gonyaulax and the alga Chlamydomonas. Since Chlamydomonas has a well defined phototactic rhythm, and its genetic system has already been described, it is being used to select and analyze rhythm mutants, especially with regard to the biochemical nature of lesions associated with specific phenotypes. Up to now there are no clearly defined biochemical correlates of rhythmicity in this cell; these studies may provide new information along these lines. With Gonyaulax on the other hand we do have a well defined biochemical correlate of the in vivo rhythm of bioluminescence: the luciferase activity in extracts varies with time of day in concert with the rhythm. As the first step in obtaining an understanding of the control mechanism we are continuing to explore the nature of this activity change - whether by synthesis and destruction or by a cycle of activation and inhibition. The situation is complicated by the fact that luciferase occurs in an array of molecular sizes, whose interrelationship and functional importance is under investigation. Ultrastructural aspects of the luminescence system are also being investigated.